Dysregulation of NGF-signaling and Egr-1 expression by Tat in neuronal cell culture

Cultured Cell Line Models of Neuronal Differentiation: NT2, PC12, and SK-N-MC

The lack of a convenient, easily maintained, and inexpensive in vitro human neuronal model to study neurodegenerative diseases prompted us to develop a rapid, 1-h differentiated neuronal cell model based on human NT2 cells and C3 transferase. Here, we describe the rapid differentiation of human neuronal NT2 cells, and the differentiation, transduction, and transfection of human SK-N-MC cells and rat PC12 cells to obtain cells with the morphology of differentiated neurons that can express exogenous genes of interest at high level.

The delicate balance between neurotoxicity and neuroprotection in the context of HIV-1 infection

Human immunodeficiency virus type-1 (HIV-1) causes a spectrum of neurological impairments, termed HIV-associated neurocognitive disorder (HAND), following the infiltration of infected cells into the brain. Even though the implementation of antiretroviral therapy reduced the systemic viral load, the prevalence of HAND remains unchanged and infected patients develop persisting neurological disturbances affecting their quality of life. As a result, HAND have gained importance in basic and clinical researches, warranting the need of developing new adjunctive treatments. Nonetheless, a better understanding of the molecular and cellular mechanisms remains necessary. Several studies consolidated their efforts into elucidating the neurotoxic signaling leading to HAND including the deleterious actions of HIV-1 viral proteins and inflammatory mediators. However, the scope of these studies is not sufficient to address all the complexity related to HAND development. Fewer studies focused on an altered neuroprotective capacity of the brain to respond to HIV-1 infection. Neurotrophic factors are endogenous polyproteins involved in neuronal survival, synaptic plasticity, and neurogenesis. Any defects in the processing or production of these crucial factors might compose a risk factor rendering the brain more vulnerable to neuronal damages. Due to their essential roles, they have been investigated for their diverse interplays with HIV-1 infection. In this review, we present a complete description of the neurotrophic factors involved in HAND. We discuss emerging concepts for their therapeutic applications and summarize the complex mechanisms that down-regulate their production in favor of a neurotoxic environment. For certain factors, we finally address opposing roles that rather lead to increased inflammation.

Production of human antibodies by in vitro immunization using a fusion protein containing the transcriptional transactivator of HIV-1

Antigen-specific activation of human B cells represents a key step for the production of monoclonal antibodies. Several approaches have been developed over the last thirty years in order to improve the process of lymphocyte activation in vitro. In the present study, we investigated whether the transcriptional transactivator (Tat) of human immunodeficiency virus, which possesses numerous biological activities, is able to trigger antibody secretion when incubated with human peripheral blood mononuclear cells. No such effect was observed when using Tat as a free protein. However, we found a significant IgM antibody production when Tat was previously fused to a double domain, called ZZ, derived from protein A of Staphylococcus aureus. The effect was also observed when the fusion protein, called ZZTat101, was incubated with purified B cells, indicating that the phenomenon does not require T-cell help. Antibody secretion was observed in the absence of cytokines that are usually used during in vitro immunization experiments, indicating that ZZTat101 provides the signals required for the initiation of the immune response. Antibody secretion was observed using a ZZTat mutant, containing only the Tat residues 22 to 57, called ZZTat22-57, indicating that this region is sufficient to initiate the immune response. In contrast, the effect was not found with a ZZTat22-57 mutant devoid of the seven Tat cysteines located between residues 22 and 37, demonstrating that these residues play a crucial role in the phenomenon. Our results pave the way to the development of a new in vitro immunization method based on antigens associated with ZZTat.

Cultured cell line models of neuronal differentiation: NT2, PC12

The lack of a convenient, easily maintained and inexpensive in vitro human neuronal model to study neurodegenerative diseases, prompted us to develop a rapid, 1-h differentiated neuronal cell model based on human NT2 cells and C3 transferase. Here, we describe the rapid differentiation of human neuronal NT2 cells, and the differentiation, transduction and transfection of rat PC12 cells to obtain cells with the morphology of differentiated neurons that can express exogenous genes of interest at high level.

Activation of Egr-1 expression in astrocytes by HIV-1 Tat: new insights into astrocyte-mediated Tat neurotoxicity

Human immunodeficiency virus type 1 (HIV-1) Tat plays an important role in HIV-associated neuropathogenesis; the underlying mechanisms are still evolving. We have recently shown that HIV-1 Tat induces expression of glial fibrillary acidic protein (GFAP), a characteristic of HIV-1 infection of the central nervous system. We have also shown that the Tat-induced GFAP expression in astrocytes is regulated by p300 and that deletion of the early growth response 1 (Egr-1) cis-transacting element within the p300 promoter abolishes Tat-induced GFAP expression. In this study, we further examined the relationship between Tat and Egr-1 in astrocytes. We found increased Egr-1 protein expression in Tat-expressing human astrocytoma cells and mouse primary astrocytes. Using the Egr-1 promoter-driven firefly luciferase reporter gene assay and the site-directed mutagenesis, we demonstrated that Tat increased Egr-1 expression by transactivating the Egr-1 promoter and involving specific serum response elements within the promoter. Consistent with these data, we showed that Tat transactivation of the Egr-1 promoter was abrogated when astrocytes were cultured in serum-reduced media. Taken together, these results reveal that Tat directly transactivates Egr-1 expression and suggest that Tat interaction with Egr-1 is probably one of the very upstream molecular events that initiate Tat-induced astrocyte dysfunction and subsequent Tat neurotoxicity.

Peptide therapy with pentadecapeptide BPC 157 in traumatic nerve injury

We focused on the healing of rat transected sciatic nerve and improvement made by stable gastric pentadecapeptide BPC 157 (10 microg, 10ng/kg) applied shortly after injury (i) intraperitoneally/intragastrically/locally, at the site of anastomosis, or after (ii) non-anastomozed nerve tubing (7 mm nerve segment resected) directly into the tube. Improvement was shown clinically (autotomy), microscopically/morphometrically and functionally (EMG, one or two months post-injury, walking recovery (sciatic functional index (SFI)) at weekly intervals). BPC 157-rats exhibited faster axonal regeneration: histomorphometrically (improved presentation of neural fascicles, homogeneous regeneration pattern, increased density and size of regenerative fibers, existence of epineural and perineural regeneration, uniform target orientation of regenerative fibers, and higher proportion of neural vs. connective tissue, all fascicles in each nerve showed increased diameter of myelinated fibers, thickness of myelin sheet, number of myelinated fibers per area and myelinated fibers as a percentage of the nerve transected area and the increased blood vessels presentation), electrophysiologically (increased motor action potentials), functionally (improved SFI), the autotomy absent. Thus, BPC 157 markedly improved rat sciatic nerve healing.

An integrated systems analysis implicates EGR1 downregulation in simian immunodeficiency virus encephalitis-induced neural dysfunction

Human immunodeficiency virus (HIV)-associated dementia (HAD) is a syndrome occurring in HIV-infected patients with advanced disease that likely develops as a result of macrophage and microglial activation as well as other immune events triggered by virus in the central nervous system. The most relevant experimental model of HAD, rhesus macaques exhibiting simian immunodeficiency virus (SIV) encephalitis (SIVE), closely reproduces the human disease and has been successfully used to advance our understanding of mechanisms underlying HAD. In this study we integrate gene expression data from uninfected and SIV-infected hippocampus with a human protein interaction network and discover modules of genes whose expression patterns distinguish these two states, to facilitate identification of neuronal genes that may contribute to SIVE/HIV cognitive deficits. Using this approach we identify several downregulated candidate genes and select one, EGR1, a key molecule in hippocampus-related learning and memory, for further study. We show that EGR1 is downregulated in SIV-infected hippocampus and that it can be downregulated in differentiated human neuroblastoma cells by treatment with CCL8, a product of activated microglia. Integration of expression data with protein interaction data to discover discriminatory modules of interacting proteins can be usefully used to prioritize differentially expressed genes for further study. Investigation of EGR1, selected in this manner, indicates that its downregulation in SIVE may occur as a consequence of the host response to infection, leading to deficits in cognition.

Evidence for modulation of BAG3 by polyomavirus JC early protein

Polyomavirus JC (JCV) infects oligodendrocytes and astrocytes in the brain and is the cause of the demyelinating disease progressive multifocal leukoencephalopathy (PML). In cell culture, JCV infection is characterized by severe damage to cellular DNA, which begins early in infection, and a viral cytopathic effect, which is observed late in infection. Nevertheless, these JCV-infected cells show a low level of apoptosis, at both the early and late stages of infection. This suggests that there is conflicting interplay between viral anti-apoptotic pathways that seek to optimize virus production, e.g. through T antigen (T-Ag)-p53 interaction, and cellular pro-apoptotic pathways that seek to eliminate virally infected cells. The apoptosis regulatory protein BAG3 is a member of the human Bcl-2-associated athanogene (BAG) family of proteins, which function as molecular co-chaperones through their interaction with Hsc70/Hsp70 and function in the regulation of the cellular stress response, proliferation and apoptosis. This study showed that BAG3 protein is downregulated upon JCV infection and that this effect is mediated by JCV T-Ag via repression of the BAG3 promoter. The site of action of T-Ag was mapped to an AP2 site in the BAG3 promoter, and gel shift and chromatin immunoprecipitation assays showed that T-Ag inhibited AP2 binding to this site, resulting in downregulation of BAG3 promoter expression. Using BAG3 and T-Ag expression and BAG3 siRNA, it was found that BAG3 and T-Ag had antagonistic effects on the induction of apoptosis, being anti-apoptotic and pro-apoptotic, respectively. The significance of these interactions to the JCV life cycle is discussed.

Molecular mechanism(s) involved in the synergistic induction of CXCL10 by human immunodeficiency virus type 1 Tat and interferon-gamma in macrophages

Synergistic interactions between viral proteins and soluble host factors released from infected mononuclear phagocytes play a critical role in the pathogenesis of human immunodeficiency virus (HIV)-associated dementia (HAD). The chemokine CXCL10 has been found to be closely associated with the progression of HIV-1-related central nervous system (CNS) disease and its related neuropsychiatric impairment. In this report the authors demonstrate that the HIV-1 protein Tat can interact with the proinflammatory cytokine interferon (IFN)-gamma to dramatically induce the expression of CXCL10 in macrophages. Synergistic induction of CXCL10 by both Tat and IFN-gamma was susceptible to inhibition by the MEK1/2 inhibitor U0126 and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. In addition, JAK/STAT pathway plays a major role in Tat/gamma-mediated CXCL10 induction in macrophages because pretreatment of stimulated macrophages with JAK inhibitor completely abrogated the synergistic induction of the chemokine. Functionality of the synergistically induced CXCL10 was further demonstrated by its chemotactic activity for peripheral blood lymphocytes. Taken together, these findings demonstrate that the cooperative interaction of Tat and IFN-gamma results in enhanced chemokine expression, which in turn can amplify the inflammatory responses within the CNS of HAD patients by recruiting more lymphocytes in the brain.

HIV-1 Tat inhibits NGF-induced Egr-1 transcriptional activity and consequent p35 expression in neural cells

Infection with HIV-1 causes degeneration of neurons leading to motor and cognitive dysfunction in AIDS patients. One of the key viral regulatory proteins, Tat, which is released by infected cells, can be taken up by various uninfected cells including neurons and by dysregulating several biological events induces cell injury and death. In earlier studies, we demonstrated that treatment of neuronal cells with Tat affects the nerve growth factor (NGF) signaling pathway involving MAPK/ERK. Here we demonstrate that a decrease in the level of Egr-1, one of the targets for MAPK, by Tat has a negative impact on the level of p35 expression in NGF-treated neural cells. Further, we demonstrate a reduced level of Egr-1 association with the p35 promoter sequence in NGF-treated cells expressing Tat. As p35, by associating with Cdk5, phosphorylates several neuronal proteins including neurofilaments and plays a role in neuronal differentiation and survival, we examined kinase activity of p35 complexes obtained from cells expressing Tat. Results from H1 kinase assays showed reduced activity of the p35 complex from Tat-expressing cells in comparison to that from control cells. Accordingly, the level of phosphorylated neurofilaments was diminished in Tat-expressing cells. Similarly, treatment of PC12 cells with Tat protein or supernatant from HIV-1 infected cells decreased kinase activity of p35 in these cells. These observations ascribe a role for Tat in altering p35 expression and its activity that affects phosphorylation of proteins involved in neuronal cell survival.